There have been known as a relative art of the present invention capacity control valves for a variable displacement type compressor. In the displacement control valve, a valve body is mounted to an actuation rod and the valve body opens and closes its valve in accordance with the actuation of a solenoid rod in a solenoid portion. The solenoid rod is connected to a movable iron core that is retained in a bore placed in a mating fixed iron core in a freely slidable manner (for example, see FIG. 1 shown in Japanese Unexamined Patent Publication No. 2001-342946,A).
A displacement control valve in FIG. 6 has similarity to a displacement control valve disclosed in FIG. 1 of the patent reference 1. In FIG. 6, a valve housing 105 has an axially extending through hole therein. The through hole is composed of a discharge valve hole 110C, a suction valve hole 110D, a first guide hole 110E, and a second guide hole 110F. There is formed a valve chamber 111 between the discharge valve hole 110C and the suction valve hole 110D. A first suction pressure passage 110B1 is communicated with the suction valve hole 110D while a discharge pressure passage 110A is communicated with the discharge valve hole 110C. Also shown at the bottom portion of the figure is a second suction pressure passage 110B2 which is communicated with the through hole.
The valve housing 105 has an integral construction in which a first valve housing 105A and a second valve housing 105B are joined at their end portions via screw connection. The first valve housing 105A disposes a spring chamber 120 at its end portion. The open end of the spring chamber 120 is connected to a spring seat portion 122 thereat via screw connection. There is disposed a spring 121 between the spring seat portion 122 and an actuation rod 101. Fastening the thread on the spring seat portion 122 adjusts the spring force of the spring 121. The spring 121 thus yields a resilient urging force against the actuation rod 101 in an upward direction as the figure shows.
The actuation rod 101 is placed along the through hole of the valve housing 105. The actuation rod 101 has an integral construction which is comprised of a first stopper 101E sliding against the second guide hole 110F, a valve body 101A being disposed in the valve chamber 111, and a second guide hole 110F fitting the second stopper 101F in freely slidable a manner. The end face of a solenoid rod 101C which is fitted to a rod bore 132A of a fixed iron core 132 comes to a planar contact with the end face of the actuation rod 101. Also both end faces of the valve body 101A define valve faces thereat. Opening areas of the discharge valve hole 110C and the suction valve hole 110D are modulated in an alternate manner by abutting and lifting actions of the valve faces of the valve body 101A against the valve seats which are arranged in the valve chamber 111 of the valve housing 111. Actuation of the valve body 101A in a direction opening the discharge valve hole 110C induces a rigorous flow of fluid at discharge pressure from the discharge pressure passage 110A into a crank chamber pressure passage 110G. This action, at the same time, implies the valve body 101A to move in a direction closing the suction valve hole 110D, thus reducing the outflow of fluid at suction pressure from the suction pressure passage 110B1 to the crank chamber pressure passage 110G.
The actuation rod 101 which is integral to the valve body 101A permits the first stopper 101E and the second stopper 101F, respectively, to slide against the first guide hole 110E and the second guide hole 110F. The valve face of the valve body 101A also comes into contact with and lifts off the valve seat. Therefore, the sliding resistance of the valve body 101A as well as of the first stopper 101E and the second stopper 101F needs to be reduced in order to avoid friction and wear thereof.
The other end portion of the valve housing 105 defines a solenoid portion 130. The solenoid portion 130 is comprised of a movable iron core 131, a fixed iron core 132 and a solenoid coil 135. Exciting the solenoid coil 135 actuates the movable iron core 131, which in turn moves the solenoid rod 101C. The solenoid rod 101C then undergoes a sliding motion, being guided by the rod bore 132A of the fixed iron core 132. A portion of fluid at suction pressure Ps supplied from the suction pressure passage 110B1 is permitted to flow into a movable iron core chamber 136 after passing through the clearance formed at the outer circumference of the solenoid rod 101C. This creates a balance in force at both sides thereof by equalizing the pressures within the movable iron core chamber 136 and the spring chamber 120.
This displacement control valve 100 operates in such a manner that the valve body 101A alternately opens and closes the discharge valve hole 110C and suction valve hole 110D by the action of the actuation rod 101 which is determined by an actuation force in accordance with an electric current supplied to the solenoid portion 130 and a reaction force exerted by the spring 121. The reciprocating control of the opening degrees of the discharge valve hole 110C and suction valve hole 110D by the valve body 101A allows fluid at discharge pressure Pd and fluid at suction pressure Ps to modulate a swash plate after flowing into a crank chamber of a compressor (not shown).
In the actuation rod 101 of the displacement control valve 100, the first stopper 101E and the second stopper 101F are arranged to have a common axis and thus permitted to fittingly slide against the first guide hole 110E and the second guide hole 110F of the valve housing 105, respectively. Furthermore, the respective valve faces are made orthogonal to the axis of the actuation rod 101 and brought into contact with the corresponding valve seats. The actuation rod 101, however, is still prone to bending due to its large length. Also the actuation rod 101 tends to be small in diameter. The movable iron core 131 fittingly slides against the inner diameter surface of a tube 134. Moreover, the solenoid rod 101C which is connected to the movable iron core 131 also slides against the rod bore 132A of the fixed iron core 132. This significantly increases a slide friction between the movable iron core 131 and the actuation rod 101. Then the response of the movable iron core 131 and the actuation rod 101 is likely to be affected such that when the spring 121 tries to actuate the actuation rod 101 or the solenoid portion 130 is excited, the movable iron core 131 and the actuation rod 101 will fail to act quickly enough in accordance with the urging force of the spring 121 and the electric current supplied to the solenoid portion 130. This, in turn, affects the performance of the displacement control valve 100 in controlling a compressor or the like.
In order to assure a secure contact between the flat end face of the solenoid rod 101C and another flat end face of the actuation rod 101, the axis of the solenoid rod 101C and the axis of the actuation rod 101 need to be perfectly aligned with each other. High precision machining for part assembly increases its manufacture cost. The solenoid rod 101C needs to permit fluid at suction pressure P to flow into the movable iron core chamber 136 via the clearance formed between the outer diameter surface of the solenoid rod 101C and the rod bore 132A of the fixed iron core 132, while a sliding movement has to be guaranteed under the presence of clearance therebetween. Therefore, uneven wear at the end face of the solenoid rod 101C is caused by a fluctuated sliding movement of the solenoid rod 101C which will occur depending on the dimension of the clearance formed between the outer diameter surface of the solenoid rod 101C and the rod bore 132A. In particular, a hard material cannot be used for the solenoid rod 101C and unwanted wear at the end face of the solenoid rod 101C decreases a control precision of the valve body 101A against the control fluid.    Patent reference 1: Japanese Unexamined Patent Publication No, 2001-342946,A